Hydrophone for passive acoustic monitoring

The soundscape
The marine “soundscape” is a continuously changing mosaic of sounds that originate from living organisms (communication and foraging), natural processes (breaking waves, wind, rain), and human activities (shipping, construction, and resource extraction). Listening to sound in the sea is a rich exploration of the marine environment, which includes some of the ways in which human activities may influence marine life.

Being a good listener
Because acoustic information spans a tremendous range of frequencies, we must listen across a very broad spectrum. Capturing information at the high-frequency end of this range requires that we sample sound very frequently (more than 250,000 times each second). This frequent sampling of sound across a broad spectrum generates a tremendous flow of data.

Many isolated marine acoustic recording systems rely on battery power and internal data storage. Such systems are limited in how long they can be deployed and in how long they can record each day. This hydrophone does not have these constraints because it is connected to the MARS cabled observatory, which supplies power from shore and high-speed communication to data storage on shore, thereby enabling the hydrophone to record 24 hours a day for long periods of time.

Hydrophone deployment
On July 28, 2015, a digital broadband hydrophone was connected to the MARS cabled observatory. Deployment went smoothly thanks to the ship’s crew and remotely operated vehicle (ROV) pilots. Shortly after the sound of the ROV faded from the MARS node as the ROV ascended to the ship, marine mammal vocalizations became clearly audible in the hydrophone recordings.

Figure 1. Hydrophone deployment. ROV Ventana held the system on the front shelf of a tool sled (arrow in picture at left) for its ride down to the MARS node at nearly 900 m depth. The arrow in the picture at right shows the hydrophone protruding from its tripod base that was placed 70 meters from the MARS node after spooling out its coil of cable.

During the hydrophone deployment, the remotely operated vehicle (ROV) Ventana carried the hydrophone at the front of its tool sled (arrow in picture at left) down to the MARS node (right ) at nearly 900 meters depth. The arrow in the picture at right shows the hydrophone protruding from its tripod base. The hydrophone was placed 70 meters from the MARS node and was connected to the node by a seafloor cable.

Data analysis
This little hydrophone generates big data—about 24 terabytes in one year. Understanding this voluminous and dense data requires a variety of analysis methods – from automated recognition of vocalizations by marine mammals to long-term statistical description of all sounds recorded. Automated methods that sift through the data to detect and classify vocalizations of different species are being developed and applied. This will allow examination of variations in the presence of different species in the Monterey Bay area, in relation to variations in the environment.

In addition to listening to recordings, we can also visually represent the soundscape using a spectrogram. A spectrogram quantifies sound energy as a function of frequency and time. Animation of spectrograms through time enables “soundscape visual browsing.”


Solving challenges
Taking the laboratory into the ocean
In Situ Ultraviolet Spectrophotometer
Midwater Respirometer System
Mobile flow cytometer
Enabling targeted sampling
Automated Video Event Detection
Gulper autonomous underwater vehicle
Advancing a persistent presence
Aerostat hotspot
Benthic event detectors
Benthic rover
Fault Prognostication
Long-range autonomous underwater vehicle Tethys
Marine “soundscape” for passive acoustic monitoring
Monterey Ocean-Bottom Broadband Seismometer
Shark Café camera
Vehicle Persistence
Wave Glider-based communications hotspot
Emerging and current tools
Aerostat hotspot
Wave Glider-based communications hotspot
Data management
Oceanographic Decision Support System
Spatial Temporal Oceanographic Query System (STOQS) Data
Video Annotation and Reference System
Apex profiling floats
Benthic event detectors
Deep particle image velocimetry
Environmental Sample Processor
How the ESP Works
Genomic sensors
ESP Web Portal
The ESP in the news
Investigations of imaging for midwater autonomous platforms
Lagrangian sediment traps
Laser Raman Spectroscopy
Midwater Respirometer System
Mobile flow cytometer
Smart underwater connector
Wave-Power Buoy
Vehicle technology
Benthic Rover
Gulper autonomous underwater vehicle
Imaging autonomous underwater vehicle
In Situ Ultraviolet Spectrophotometer
Seafloor mapping AUV
Long-range autonomous underwater vehicle Tethys
Mini remotely operated vehicle
ROV Doc Ricketts
ROV Ventana
Automated Video Event Detection
Deep learning
SeeStar Imaging System
Shark Café camera
Video Annotation and Reference System
Technology publications
Technology transfer


This MBARI team is working in collaboration with the Naval Postgraduate School, Stanford Hopkins Marine Station, Moss Landing Marine Laboratories, University of California at Santa Cruz, and the Monterey Bay National Marine Sanctuary.

John Ryan

Senior Research Specialist

Craig Dawe

Technical Support Manager/ MARS Manager

Ken Heller

MARS Operations Technician

Yanwu Zhang

Senior Research Specialist